The threshold voltage variations for actual size MOSFETs obtained by capacitance measurement are compared with those obtained by the current measurement, and their differences are studied for the first time. It is found that the threshold voltage variations obtained by the capacitance measurement show the similar behavior to those current measurement and the absolute value is less than those obtained by the current measurement. The reason for the difference is partially explained by that the local channel dopant non-uniformity along the current path makes the threshold voltage variation obtained from current measurement larger. It is found that the flat-band voltage variations, which are obtained from the measured C-V curves, are small and not significant to the threshold voltage variation.

A test structure for charge-based capacitance measurement (CBCM) method has been developed to evaluate the threshold voltage variability from capacitance-voltage (C-V) curves of actual size metal-oxide-semiconductor field-effect-transistors (MOSFETs). The C-V curves from accumulation to inversion are measured for the MOSFETs having various channel dimensions using this test structure. Intrinsic capacitance components between the MOSFET electrodes are extracted from those C-V curves which are considered to include parasitic capacitance component. The intrinsic C-V curves are used for attempting to extract threshold voltage variations of their MOSFETs. It is found that the developed test structure is very useful for the evaluation of MOSFETs variability, because the derivation in MOSFET C-V curves is not influenced by current measurement noise.